For example, during shutdown of a steam turbine or the like used in a power plant or the like, when a turbine rotor is left in a non-rotation state at a high temperature, bending in the turbine rotor may occur due to distortion by heating generated in the turbine rotor due to a temperature difference generated in a turbine casing in association with a decrease in temperature of steam or a gas in the turbine or the weight of the turbine rotor. Here, in order to avoid the occurrence of bending in the turbine rotor of the steam turbine, during shutdown of the swam turbine and before starting the steam turbine, turning that rotates the turbine rotor for a predetermined time at a low speed should be performed. In order to perform such turning, a turning apparatus for rotating the turbine rotor using power of an electric motor is widely used.
In such a turning apparatus, as a driving gear is meshed with a wheel gear installed at the turbine rotor and the driving gear is rotated by the electric motor, the turning of the turbine rotor is performed. Here, When starting of the steam turbine is terminated, meshing between the driving gear of the turning apparatus and the wheel gear of the turbine rotor is released and the turning is terminated. For example, in Patent Literature 1, when the wheel gear is rotated more rapidly than the turning by the turning apparatus, the wheel gear pushes the driving gear out, and the meshing between the wheel gear and the driving gear is released. In addition, in Patent Literature 2, as a hydraulic cylinder connected to the driving gear is tilted in a direction away from the wheel gear, the meshing between the wheel gear and the driving gear is released.